Oxide magnetic material and chip part

ABSTRACT

An oxide magnetic material comprising main constituents including Fe 2 O 3 , ZnO, CuO and NiO. Y 2 O 3  of 0.003 to 0.021 wt % and-ZrO 2  of 0.06 to 0.37 wt % are included in said main constituents with respect to all amounts. It is also preferable that Si of 0.010 to 0.0112 wt % is included in said main constituents with respect to all amounts. Further, it is also preferable that Y 2 O 3 of 0.001 to 0.011 wt % , ZrO 2  of 0.031 to 0.194 wt %, and Si of 0.010 to 0.056 wt % are included in said main constituents with respect to all amounts.

Background of the Invention

[0001] 1. Field of the Invention

[0002] The present invention relates to an oxide magnetic material to beused in various electronic parts, and a chip part formed with the oxidemagnetic material and including a bulk-type coil part and an internalconductor for inductance to be used in a high frequency area, as well asa method of producing the oxide magnetic material, and to a method ofproducing the chip part.

[0003] 2. Description of the Related Art

[0004] Ni—Cu—Zn based ferrite is generally used as an oxide magneticmaterial such as coil parts and the like to be used in a high frequencyarea. A powder metallurgical method is general for producing the same.According to this method, oxides such as Fe₂,₃, NiO, CuO, ZnO and thelike to be starting materials are weighed so as to be predeterminedratios, and are then dry- or wet-mixed and crushed, and this mixedpowder is temporarily baked. Subsequently the temporarily baked matteris roughly crushed and is further pulverized. In case the oxide iswet-crushed, the powder is required to be dried. Here, properties offerrite considerably depend on the composition; therefore, thedivergence of composition should be kept extremely small from theviewpoint of production control. Further, material for laminated coil isrequired to be baked at a lower temperature than the melting point ofAg, and the composition control is required to be at a level of 0.1 mol% of Fe₂O₃, NiO, Cuo or ZnO. Especially as to Fe₂O_(3,) reactivityincreases as coming near to the stoichiometrical composition of ferrite,but when exceeding it, the reactivity abruptly decreases; therefore,among the main constituents of ferrite, a most serious compositioncontrol is needed.

[0005] For conventional Ni—Cu—Zn ferrite, stainless steel balls, aluminaballs, zirconia balls and other have been used as medium beads in theproduction process, and crushed with mixing, temporarily baked, roughlycrushed and further pulverized. The bulk-type coil material is normallytemporarily baked and crashed such that a specific surface area isaround 1.0 to 6.0 m²/g. The laminated coil material is, however, crushedfor a long time because it is required to be baked at a lowertemperature than the melting point of Ag, thereby to increase thespecific surface area up to around 3.0 to 15.0 m²/g to heighten thereactivity of powder at low temperature.

[0006] Here, the stainless steel balls have Fe as a main constituent,and due to mechanochemical reaction during crushing, Fe₂O₃ which is amain constituent of Ni—Cu—Zn ferrite is increased. The increase of Fe₂O₃changes the composition of Ni—Cu—Zn ferrite and causes a stabilizedcomposition control to be difficult. That is, it is difficult to controlthe composition with weighed quality values. Other medium beads have adefect in abrasion resistibility, and a defect that abraded powders ofthe medium beads are mixed into the crushed powder as impurities.

[0007] Further, the general medium beads have the inner side of abrasionresistibility which is lower than that of the outer side. Therefore, itcauses a divergence in the composition due to the difference in mixingamount of powder produced by abrasion as the production goes on, and itis impossible to obtain stable composition. The crushing for a long timewill invite the increase of the amount of the abraded powder,deteriorating the property of baked material. Namely, the abraded powdermixed as impurities will deteriorate the sintering property of Ni—Cu—Znferrite, thereby to cause the baking temperature to be high forobtaining the density and permeability of sintered material with theneighborhood of a theoretical density. This will invite a highproduction cost and decrease of stability in products, and further willmake it difficult to bake the sintered material at lower temperaturethan the melting point of Ag.

[0008] The Japanese patent No. 2708160 discloses, for the purpose ofreducing the mix of abraded powder at the time of crushing, the use ofballs of fully stabilized zirconia (FSZ) of high abrasion resistibilityor of partially stabilized zirconia (PSZ) as medium beads for crushingMn—Zn based ferrite. According to the method of this patent document,the zirconia balls of a diameter 0.5 to 3.0 mm are used as medium beadsin the pulverizing process to extremely prevent impurities from beingmixed, thereby to suppress the mixing amount to be less than 0.02 wt %relative to the main constituent. It is described in this patentdocument that with this method, the powder may be sintered attemperature lower by about 100 to 200° C. (that is, at approximately1000° C.) in contrast to the temporarily baking temperature of 1200 ° C.or higher of the conventional art to obtain the sintered material withthe neighborhood of theoretical density, thus to industrially lower thesintering temperature and reduce the production cost. Further,JP-A-7-133150 discloses a sample having ZrO of 0.01 to 3.0 wt % relativeto the main constituent of Ni—Cu—Zn ferrite and baked at the temperatureof 1100° C. for 1.5 hours for the purpose of providing a magneticmaterial of high mechanical strength.

[0009] However, the baking temperature of approximately 1000° C.described in the Japanese patent No. 2708160 will not actually reducethe baking cost and will not be adapted to the simultaneous baking withAg of melting point of approximately 960° C. The baking temperature ofapproximately 1100° C. as described in JP-A-7-133150 will be furtherimpossible for the simultaneous baking with Ag.

[0010] Further, according to the production method of the Japanesepatent 2708160, medium beads of small diameter are used to reduce theamount of impurities mixed into the material due to the abrasion of themedium beads, and the temporarily baked material is crushed, taking along time, for example, 196 hours. Therefore, the ball efficiency([material processing amount]/[ball weight]), that is, the crashingefficiency is bad.

SUMMARY OF THE INVENTION

[0011] In consideration of the above mentioned problems, it is an objectof the invention to provide an oxide magnetic material which can besubjected to a low temperature baking with holding sintering propertyand permeability and shortening the crushing time, and to provide a chippart formed by use of the same. In addition, it is also an object of theinvention to provide a method of producing the oxide magnetic materialand a method of producing the chip part.

[0012] According to a first aspect of the invention, the oxide magneticmaterial is characterized by containing Fe₂O₃, ZnO, CuO and NiO as mainconstituents, and further containing Y₂O₃ of 0.003 to 0.021 wt % andZrO₂ of 0.06 to 0.37 wt % in the main constituents with respect to allamounts.

[0013] As additives to the main constituents, it is also preferable thatthe oxide magnetic material further contains Si of 0.010 to 0.112 wt %(including the cases where Si is contained as silicon oxide) in the mainconstituents with respect to all amounts.

[0014] Further, as additives to the main constituents, it is alsopreferable that the oxide magnetic material further contains Y₂O₃ of0.001 to 0.011 wt %, ZrO₂ of 0.03 to 0.194 wt %, and Si of 0.010 to0.056 wt % (including the cases where Si is contained as silicon oxide)in the main constituents with respect to all amounts.

[0015] So far as giving no influence to the properties such as thepermeability or the density of the baked material, Si, P, Al, B, Mn, Mg,Co, Ba, Sr, Bi, Pb, W, V, Mo and the like may be included as impurities.For obtaining a permeability higher than a predetermined value, thecomposition of main constituents is preferably Fe₂O₃of 40 to 51 mol %,ZnO of 1 to 34 mol %, CuO of 1 to 30 mol % and the balance being NiO.More preferably, Fe₂O₃ is 46 to 50 mol %, ZnO is 32 to 34 mol %, CuO is9 to 11 mol % and NiO is 8 to 11 mol %.

[0016] In case the partially stabilized zirconia ball (PSZ) containingY₂O₃ is used to crush the temporarily baked powder, it is known that thepartly stabilized zirconia ball having Y₂O₃ containing about 3 mol % ismost excellent in hardness and destructive toughness value (StrongZirconia-Tough Ceramics, written by HORI, Saburou, issued from UchidaRoukakuen) . For trying to obtain the crushed powder of average particlediameter of approximately 0.1 to 1.0 μm, if the composition is Y₂O₃ ofless than 0.003 wt % and ZrO₂ of less than 0.06 wt %, it is required tocrush the powder, delaying an agitating rate and taking a long time.However, if the composition is more than these weight percents, thecrushing efficiency may be heightened and the crushing is possible at ashorter time, though depending on the size of ball diameter andagitating rate. On the other hand, if Y₂O₃ exceeds 0.021 wt % and ZrO₂exceeds 0.37 wt %, it is difficult to obtain an apparent density of 5.0g/cm³ or more which is said to be not problematical about the physicalstrength at 920 ° C. where a simultaneous baking with Ag is possible.Therefore, the baking temperature should be raised in order to securethe apparent density. Further, if Y₂O₃ exceeds 0.021 wt % and ZrO₂exceeds 0.37 wt %, the permeability may be deteriorated.

[0017] In the case where the oxide magnetic material further contains Sias additives to the main constituents, for trying to obtain the crushedpowder of average particle diameter of approximately 0.1 to 1.0 μm, ifthe composition is Si of less than 0.010 wt %, it is required to crushthe powder, delaying an agitating rate and taking a long time. However,if the composition is more than these weight percents, the crushingefficiency may be heightened and the crushing is possible at a shortertime, though depending on the size of ball diameter and agitating rate.On the other hand, if Si exceeds 0.112 wt %, it is difficult to obtainan apparent density of 5.0 g/cm³ or more which is said to be notproblematical about the physical strength at 920° C. where asimultaneous baking with Ag is possible. Therefore, the bakingtemperature should be raised in order to secure the apparent density.Further, if Si exceeds 0.112 wt %, the permeability may be deteriorated.

[0018] In the case where the oxide magnetic material further containsY₂O₃, ZrO₂, and Si as additives to the main constituents, for trying toobtain the crushed powder of average particle diameter of approximately0.1 to 1.0 μm, if the composition is Y₂O₃ of less than 0.001 wt % andZrO₂ of less than 0.031 wt %, and Si of less than 0.010 wt %, it isrequired to crush the powder, delaying an agitating rate and taking along time. However, if the composition is more than these weightpercents, the crushing efficiency may be heightened and the crushing ispossible at a shorter time, though depending on the size of balldiameter and agitating rate. On the other hand, if Y₂O₃ exceeds 0.011 wt% and ZrO₂ exceeds 0.37 wt % and Si exceeds 0.056 wt %, respectively, itis difficult to obtain an apparent density of 5.0 g/cm³ or more which issaid to be not problematical about the physical strength at 920° C.where a simultaneous baking with Ag is possible. Therefore, the bakingtemperature should be raised in order to secure the apparent density.Further, if Y₂O₃ exceeds 0.011 wt % and ZrO₂ exceeds 0.194 wt % and Siexceeds 0.056 wt %, the permeability may be deteriorated.

[0019] A chip part according to a second aspect of the invention ischaracterized by using a sintered material of the oxide magneticmaterial which is described in the first aspect of the invention so asto be formed as a bulk-type coil part.

[0020] As the chip part according to the second aspect is composed byusing the oxide magnetic material which is defined in the first aspectof the invention, the chip part is baked at a low temperature and isprovided at a low cost while sufficiently coping with the one baked at ahigh baking temperature with respect to the strength and permeability.

[0021] A chip part according to a third aspect of the invention ischaracterized by using the sintered material of the oxide magneticmaterial according to the first aspect, and having an electric conductorlayer in the sinteredmaterial, the chip part having a laminated coilpart or partly having the laminated coil part.

[0022] The chip part according to a fourth aspect of the invention ischaracterized in that an internal conductor has Ag or an alloy of Ag andPd as a main constituent in the tip part according to the third aspect.

[0023] As the chip part according to the third and fourth aspect of theinvention is formed by use of the oxide magnetic material according tothe first aspect, the chip part has substantially the same strength andpermeability as the chip part according to the second aspect, andfurther can be baked simultaneously with Ag and the alloy of Ag—Pd.

[0024] A fifth aspect of the invention is that a method for producingthe oxide magnetic material according to the first aspect, characterizedin that medium beads of partially stabilized zirconia are used at a timeof mixing and crushing raw material and at a time of crushing atemporarily baked material, and Y₂O₃of 0.003 to 0.021 wt % and ZrO₂ of0.06 to 0.37 wt % is contained therein with respect to all amounts inthe oxide magnetic material by wear of the medium beads.

[0025] Thus, if the partially stabilized zirconia balls is used to crushthe material after being temporarily baked, it is possible to eliminatethe difficult problem in the composition control as using theconventional stainless steel balls or the like. Further, since Y₂O₃ andZrO₂ are mixed into the material through the crushing process, theprocess for weighing and mixing the constituent into the material may beeliminated.

[0026] In the fifth aspect of the invention, it is also preferable thatsilicon nitride is used as medium beads and that Si of 0.010 to 0.112 wt% is contained with respect to all amounts in the oxide magneticmaterial by wear of the medium beads.

[0027] Thus, if the silicon nitride balls are used to crush the materialafter being temporarily baked, it is possible to eliminate the difficultproblem in the composition control as using the conventional stainlesssteel balls or the like. Further, since Si is mixed into the materialthrough the crushing process, the process for weighing and mixing theconstituent into the material may be eliminated.

[0028] Further, in the fifth aspect of the invention, it is alsopreferable that partially stabilized zirconia and silicon nitride areused as medium beads at a time of mixing and crushing raw material andat a time of crushing a temporarily baked material by means of the mediaagitating mill of the wet internal circulation type. By wear of themedium beads, Y_(2 O) ₃ of 0.001 to 0.011 wt %, ZrO₂ of 0.03 to 0.194 wt%, and Si of 0.010 to 0.056 wt % are contained with respect to allamounts in the oxide magnetic material.

[0029] Thus, if balls of partially stabilized zirconia and siliconnitride are used to crush the material after being temporarily baked, itis possible to eliminate the difficult problem in the compositioncontrol as using the conventional stainless steel balls or the like.Further, since Y₂O₃, ZrO₂, and Si are mixed into the material throughthe crushing process, the process for weighing and mixing theconstituent into the material may be eliminated.

[0030] Moreover, in the fifth aspect of the present invention, it ispreferable that the volume ratio of the silicon nitride beads is in therange between 20% and 99% with respect to the total amount of partiallystabilized zirconia beads and silicon nitride beads.

[0031] Due to the above ratio of partially stabilized zirconia beads andsilicon nitride beads, mixing of ZrO₂ and Y₂O₃, which are mainconstituents of partially stabilized zirconia beads, is furtherfacilitated by means of wear of the medium beads, compared with the casewhere only partially stabilized zirconia beads are used to crush thematerial.

[0032] According to a sixth aspect of the invention, a method forproducing the oxide magnetic material in the fifth aspect ischaracterized by using material as medium beads having diameter of 0.2to 5 mm.

[0033] In the case where the medium beads are of a diameter less than0.2 mm, the crushing efficiency is lowered. On the other hand, in thecase where the diameter exceeds 5 mm, the powder will not besufficiently pulverized, and the sintering temperature will become highfor obtaining a density of sintered material with the neighborhood oftheoretical density and the permeability will be deteriorated.

[0034] According to a seventh aspect of the invention, a method forproducing the oxide magnetic material in the fifth or sixth aspect ischaracterized in that agitating rate of the medium beads is 2.0 to 8.0m/s.

[0035] In the cage where the agitating rate of the medium beads is lowerthan 2.0 m/s, it will take a long time to crush the material until adesired specific surface area is obtained. This is not reasonable inconsideration of the lead time pertaining to the production of material.On the other hand, if exceeding 8.0 m/s, the abrasion of beads isincreased, and the baking temperature becomes high for obtaining thedensity of a sintered material with the neighborhood of the theoreticaldensity and a desired permeability, inviting the increase of productioncost, the lowering of stabilization of products, and further making itdifficult to bake the material at a temperature lower than the meltingpoint of Ag.

[0036] According to an eighth aspect of the invention, the method in oneof fifth to seventh aspects is characterized by obtaining powders ofspecific surface area of 6.0 to 15.0 m²/g by crushing from the materialafter having been temporarily baked.

[0037] In the case where the specific surface area is less than 6.0m²/g, the baking temperature becomes high for obtaining the density ofthe sintered material in the neighborhood of the theoretical density,inviting the deterioration of the permeability. In the case where it ismore than 15.0 m²/g, the crushing time will be long.

[0038] According to a ninth aspect of the invention, the method in thethird or fourth aspect is characterized by forming an oxide magneticmaterial crushed by medium beads and an internal conductor and by bakingat a certain temperature range. If partially stabilized zirconia is usedas medium beads, the temperature range is between 880 and 920° C. Ifsilicon nitride is used as medium beads, the temperature range isbetween 910 and 920° C. If partially stabilized zirconia and siliconnitride are used as medium beads, the temperature range is between 910and 920° C.

[0039] In the case where the baking temperature is lower than the aboverange, the sintering is insufficient. In the case where exceeding theabove range, the electrode material is diffused in ferrite to extremelydeteriorate the magnetic property of chip. In this method, the bakingtime is about 5 minutes to 3 hours.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] The oxide magnetic material for a bulk-type coil part or alaminated coil part or other electronic parts according to the inventionis a ferrite material containing the main constituents of Fe₂O₃ZnO, NiO,and CuO, and containing, if needed, the slight amounts of weighedadditives such as Si, P, Al, B, Mn, Mg, Co, Ba, Sr, Bi, Pb, W, V, Mo andthe like, and further containing, as sub-constituents, ZrO₂and Y₂O₃which are mixed into the material due to abrasion of partiallystabilized zirconia balls as the medium beads. It is also preferablethat the ferrite material further contains, as sub-constituents, Siwhich is mixed into the material due to abrasion of silicon nitrideballs as the medium beads. Furthermore, it is also preferable that theferrite material further contains, as sub-constituents, ZrO₂, Y₂O₃, andSi which are mixed into the material due to abrasion of partiallystabilized zirconia balls and silicon nitride balls as the medium beads.With adjustment of the particle size of the medium beads, agitatingrate, agitating time at time of crushing raw materials and at time ofcrushing the material after being temporarily baked, the mixing amountof the medium beads is adjusted, and the baking temperature is notrequired to be heightened. Therefore, the baking may be available attemperature lower than the melting point of Ag.

[0041] The materials weighed as mentioned above are mixed and crushed bymeans of the media agitating mill of the wet internal circulation typewith at least one of the partially stabilized zirconia balls and siliconnitride balls as the medium beads. Subsequently, the crushed material istemporarily baked and crushed by means of the media agitating mill ofthe wet internal circulation type with the partially stabilized zirconiaballs as the medium beads, thereby to obtain the oxide magneticmaterial.

[0042] A core for the bulk-type coil is made up by adding a binder tothe oxide magnetic material produced as mentioned above and isgranulated, followed by molding into a predetermined shape, processedand baked at 900 to 1300° C. in the air. The core may be processed afterbaking. The core is made by winding a wire therearound, the wire beingof Au, Ag, Cu, Fe, Pt, Sn, Ni, Pb, Al, Co or an alloy thereof.

[0043] On the other hand, the laminated coil is normally produced bylaminating into one body a paste of the magnetic layer of the oxidemagnetic material and an internal conductor layer by means of a thickfilming technique (printing process or the doctor blade method), thenbaking, subsequently printing the thus obtained sintered material on thesurface thereof with a paste of an external electrode and baking. Theinternal conductor paste contains normally an electrically conductiveelement, a binder and a solvent. The material for the electricallyconductive element is preferred to be an alloy of Ag—Pd for a reason ofincreasing the quality coefficients Q of inductor. The baking conditionand baking atmosphere may be appropriately determined in considerationof the property and other of the magnetic material and electricallyconductive element, and the baking temperature is preferred to beapproximately 800 to 950° C . More preferably, the baking temperature isabout 880 to 920° C. in the case where the partially stabilized zirconiaballs are used as medium beads and about 910 to 920° C. in the casewhere silicon nitride balls or both the partially stabilized zirconiaballs and silicon nitride balls are used.

EXAMPLE 1

[0044] Now, a first example of the preferred embodiments is describedhereinafter.

[0045] Weighing and Crushing

[0046] The composition of NiO8.7 mol %, CuO 10.0mol %, ZnO 32.0 mol %,and Fe₂O₃ 49.3 mol % as the main constituent of Ni—Cu—Zn ferrite waswet-mixed with partially stabilized zirconia (PSZ) of 3 mm in diameteras medium beads by means of the media agitating mill of the wet internalcirculation type, and was dried, followed by temporarily baking at 800°C. Subsequently, the temporarily baked material was pulverized by meansof the media agitating mill of the wet internal circulation type by useof PSZ as medium beads and with the density of the temporarily basedmaterial being 33% as shown in Table 1 in that the agitating rate,crushing time and ball diameter were varied as parameters as shown inthe left end column of Table 1.

[0047] Namely, as to the samples 1 to 9, the diameter of medium beadswas 3 mm, and, the agitating rates were varied as 1 m/s, 2.0 m/s, 4.0m/s, 4.3 m/s, 5.0 m/s, 6.0 m/s, 7.0 m/s, 8.0 m/s, and 10 m/s such thatthe average particle diameters of the materials were 0.5 μm, that is,the specific surface area were 8 m²/g, while in connection with therespective agitating rates, the crushing times were varied as 76 hours,67 hours, 45 hours, 38 hours, 33 hours, 23 hours, 17 hours, 10 hours,and 2 hours. Those were made the samples 1 to 9, in which all thepowders with particles of 0.5 μm in average diameter and with specificrelative surface area of 8 m²/g were obtained.

[0048] As to the samples 10 to 13, the diameter of the ball was 3 mm andthe agitating rate was 4 m/s while the crushing times were varied as 1hour, 1.5 hours, 93 hours, and 108 hours, and the powders of averageparticles being 2.0 μm, 1.5 m, 0.3 μm, 0.2 μm, and the specific surfaceareas being 2 m²/g, 2.5 m²/g, 15 m²/g, and 17 m²/g were obtained.

[0049] As to the samples 14 to 16, the agitating rate was 4 m/s and thecrushing time was 45 hours constant while diameters of the balls werevaried as 0.2 mm, 5 mm, and 12 mm, and the powders of average particlesbeing 0.6 μm, 0.7 μm, and 1.4 μm, and relative surface areas being 7m²/g, 6 m²/g, and 3 m²/g were obtained respectively.

[0050] Further, for the purpose of comparison, the tests were carriedout as to the conventional samples 17 to 19. The sample 17 contained themain constituents of NiO 9.5 mol %, CuO 10.5 mol %, ZnO 34.0 mol %, andFe₂O₃ 46.0 mol %. The crushing machine was the media agitating mill ofthe wet internal circulation type. The balls were 3 mm in diameter andmade of stainless steel. The agitating rate and crushing time werepredetermined so that the average particle diameter of 0.5 μm and thespecific surface area of 8 m²/g might be obtained as in the case of thesamples 1 to 9.

[0051] The sample 18 was of the main constituents such as used in thesamples 1 to 16. The crushing machine was the media agitating mill ofthe wet internal circulation type. The balls were 3 mm in diameter andmade of titania. The agitating rate and the crushing time weredetermined so that the average particle diameter of 0.5 μm and thespecific surface area of 8 m²/g might be obtained as in the samples 1 to9.

[0052] The sample 19 was of the main constituents of NiO 9.5 mol %, CuO10.5 mol %, ZnO 34.0 mol %, and Fe₂O₃ 46.0 mol %. The crushing machinewas the ball mill. The balls were 3 mm in diameter and made of thestainless steel. The powder of average particles 0.3 μm, and thespecific surface area 12 m²/g was obtained. As to the samples 17 to 19,mixing and crushing before the temporarily baking of the raw materialwere carried out in wet by means of the respective media.

[0053] Impurities and mixing amount thereof in the materials shown inTable 1 and the quantitative analysis of the main constituents afterproduction shown in Table 2 were measured by the fluorescent X-raysanalysis method. The specific surface area was measured by means of FlowSoap 2300-type which is Automatic Measuring Instrument For SpecificSurface Area of Fluidization Type of (K. K.) Shimazu Seisakusyo. Theaverage particle diameter was measured by the laser diffraction andscattering method of Microtrack HRA9320-X100-type of HONEWELL.

[0054] Production of Test Samples for Measuring Permeability and Densityof Sintered Materials

[0055] 10 wt parts of 3% water solvent of PVA124 was added as a binderto the materials shown in the samples 1 to 19 to make particles. Then,the materials were molded into predetermined shapes under the measuringconditions as later described and were baked for 2 hours in the air atthe temperatures 870° C., 880° C., 910° C., 920° C., 940° C., 1000° C.,and 1100° C.

[0056] Evaluation

[0057] The core materials were evaluated with respect to the crushingtime until desired relative surface area were obtained, the confirmationof impurities which might be considered to have been mixed due toabrasion of the medium beads, the divergence in the composition of themain constituents of Fe₂O₃ ZnO, CuO, and NiO, the initial permeabilityshown in Table 3, and the apparent densities shown in Table 4. Theinitial permeability was measured by molding the material into atoroidal shape of 18 mm outer diameter, 10mm inner diameter, 3.1 mmheight, baking the molded material at a predetermined temperature in theair, forming a coil by winding a wire 20 times around the bakedmaterial, applying a field of 0.4 A/m by means of Impedance Analyzer(4291A made by Hullet Packard), measuring the inductance of 100 kHz, andcalculating the constants obtained from the shape.

[0058] The apparent density was sought by calculating a volume with thedimensions of sintered material, and dividing the mass by the volume.Herein, the apparent density was for evaluating the sintered conditionof the sintered material. If the apparent density is low, the sinteredmaterial has many air halls contained therein. If such a material isused as an element, the air hall causes to affect influences toreliability as a short-circuit and further lack the physical strength byusing at high temperature and humidity. The apparent density free ofsuch problems is generally 5.0 g/cm³ or higher which is 95% or higher ofthe theoretical density (5.3 to 5.5 g/cm³) of Ni—Cu—Zn ferrite. TABLE 1Aver- age Crush- Ball Agita- Crush- grain Speci- ing diam- ting ingdiam- fic Main impurities and ma- Ball eter rate time eter area mixingamounts (wt %) chine materials (mm) (m/s) (hr) (μm) (m²/g) ZrO₂ Y₂O₃Fe₂O₃ TiO₂ Al₂O₃ SiO₂ MoO₃ Crush- Sample 1 A* PSZ 3 1.0 76 0.5 8 0.010.001 — — — — — ing Sample 2 A PSZ 3 2.0 67 0.5 8 0.06 0.003 — — — — —rate Sample 3 A PSZ 3 4.0 45 0.5 6 0.12 0.007 — — — — — Sample 4 A PSZ 34.3 38 0.5 8 0.15 0.008 — — — — — Sample 5 A PSZ 3 5.0 33 0.5 8 0.170.011 — — — — — Sample 6 A PSZ 3 6.0 23 0.5 8 0.22 0.012 — — — — —Sample 7 A PSZ 3 7.0 17 0.5 8 0.31 0.016 — — — — — Sample 8 A PSZ 3 8.010 0.5 8 0.37 0.021 — — — — — Sample 9 A PSZ 3 10.0 2 0.5 8 0.60 0.031 —— — — — Crush- Sample 10 A PSZ 3 4.0 1 2.0 2 0.02 0.001 — — — — — ingSample 11 A PSZ 3 4.0 1.5 1.5 2.5 0.02 0.001 — — — — — Time Sample 12 APSZ 3 4.0 93 0.3 15 0.24 0.014 — — — — — Sample 13 A PSZ 3 4.0 108 0.217 0.27 0.016 — — — — — Ball Sample 14 A PSZ 0.2 4.0 45 0.6 7 0.10 0.006— — — — — diam- Sample 15 A PSZ 5 4.0 45 0.7 6 0.17 0.010 — — — — — eterSample 16 A PSZ 12 4.0 45 1.4 3 0.60 0.035 — — — — — Conven- Sample 11 AStainless 3 5.0 20 0.5 8 — — 8.12 — — 0.015 0.002 tional steel exampleSample 18 A Titania 3 5.0 38 0.5 8 — — — 0.88 0.22 0.061 0.003 Sample 19B* Stainless 3 192 0.3 12 — — 8.63 — — 0.020 0.004 steel

[0059] TABLE 2 Weighed quality values and change of composition afterproduction Weighed quality Completion Fe₂O₃ ZnO NiO CuO Fe₂O₃ ZnO NiOCuO Sample 1 49.3 32.0 8.7 10.0 49.21 32.07 8.73 9.99 Sample 2 49.3 32.08.7 10.0 49.22 32.05 8.78 9.95 Sample 3 49.3 32.0 8.7 10.0 49.21 32.068.77 9.96 Sample 4 49.3 32.0 8.7 10.0 49.26 32.04 8.72 9.98 Sample 549.3 32.0 8.7 10.0 49.22 32.08 8.72 9.98 Sample 6 49.3 32.0 8.7 10.049.23 32.05 8.76 9.96 Sample 7 49.3 32.0 8.7 10.0 49.25 32.06 8.71 9.98Sample 8 49.3 32.0 8.7 10.0 49.26 32.04 8.71 9.99 Sample 9 49.3 32.0 8.710.0 49.28 32.05 8.72 9.95 Sample 10 49.3 32.0 8.7 10.0 49.21 32.05 8.789.96 Sample 11 49.3 32.0 8.7 10.0 49.23 32.04 8.78 9.95 Sample 12 49.332.0 8.7 10.0 49.25 32.06 8.75 9.94 Sample 13 49.3 32.0 8.7 10.0 49.2832.04 8.72 9.96 Sample 14 49.3 32.0 8.7 10.0 49.26 32.06 8.71 9.97Sample 15 49.3 32.0 8.7 10.0 49.28 32.04 8.72 9.96 Sample 16 49.3 32.08.7 10.0 49.29 32.03 8.70 9.98 Sample 17 46.0 34.0 9.5 10.5 49.02 32.108.97 9.91 Sample 18 49.3 32.0 8.7 10.0 49.34 31.90 8.73 9.92 Sample 1946.0 34.0 9.5 10.5 49.20 31.99 8.94 9.88

[0060] Results of Evaluation

[0061] [Mix of Impurities]

[0062] In the case where a desired specific surface area is 8 m²/g as insamples 1 to 9 in Table 1, the crushing time is shortened as theagitating rate increases. It is, therefore, understood that theagitating rate is increased to heighten the crushing efficiency.However, the increasing of the agitating rate increases the abrasionamount of the medium beads. As to PSZ, the main constituents ZrO₂ andY₂O₃ are mixed into the material, but mixture of other constituents isnot recognized.

[0063] On the other hand, as to the samples 17 and 18 of theconventional examples, when comparing with the sample 5 of the same balldiameter and agitating rate with respect to the pulverizing time and theabrasion amount of the balls, in the case of the sample 17, namely inthe case of the stainless steel, the crushing time is shortened morethan the case of PSZ and the crushing efficiency is very high, but theabrasion quantity is very much as about 45 times of PSZ. The sample 18,namely the case of titania, the abrasion amount is about 6.5 times ofPSZ.

[0064] Divergence in the Composition Due to Mixed Impurities

[0065] Table 2 shows the divergences of the composition of the materialfrom weighing Fe₂O₃, ZnO, CuO, and NiO as the main constituents, thematerials having been mixed, crushed, temporarily baked and pulverized.These are the results of the quantitative analysis of the respectiveoxides. As is seen in Table 2, in the case where the stainless steel isused for medium beads as the samples 17 and 19, the divergence of Fe₂O₃is remarkable from weighing to completion, and in Ni—Cu—Zn ferrite, thecomposition of Fe₂O₃ which requires a most serious control, increases by3 mol % or higher from the weighing to the completion. Further since thestainless steel is different in hardness as to the outer part and innerpart, the medium beads used for a long time will cause a difference inthe mixed amount of Fe₂O₃. This indicates the difficulty of thecomposition control.

[0066] Relation Between Crushing Time and Relative Surface Area

[0067] Further as is understood from the samples 10 to 13, the specificsurface area is increased by prolonging the crushing time.

[0068] Relation Between Diameters of Balls and Relative Surface Area

[0069] Further as shown in the samples 3, 14, 15 and 16 wherein theagitating rate and crushing time are constant, in the case of the sameagitating rate and the same pulverizing time, the surface area of thepowder where the ball diameter is 3 mm is largest and the crushingefficiency is high. It is generally known that the crushing efficiencybecomes higher as the ball diameter is smaller. This is, however, thecase that a rough crushing process intervenes, and in the example wherethe rough crushing is not sufficient, it can be seen that the ball of 3mm in diameter will exhibit a highest crushing efficiency. If a ballmill is used as in the sample 19, the specific surface area is able tobe 12 m²/g with the crushing for a long time as 192 hours. However, thisrequires a crushing time more than twice of the sample 12 where the wetinternal circulation media agitating mill is operated at the agitatingrate 4 m/s. Moreover, in the case of the sample 19, it can be seen thatthe specific surface area is small and the crushing efficiency of theball mill is low.

[0070] Initial Permeability and Apparent Density

[0071] It can be seen that the permeability shown in Table 3 is inrelation to the apparent densities shown in Table 4. Namely, in thesamples 9 toll, 16, and 18 where the permeability is relatively low, theapparent density is also low. In the samples 1 to 9, PSZ ball of 3 mm indiameter was used as the medium beads and the wet internal circulationmedia agitating mill was operated to vary the agitating rate forobtaining the specific surface area 8 m²/g, but both of the permeabilityand the density of the sintered material were deteriorated when theagitating rate was heightened. This is because the increase of mixingamount of ZrO₂ and Y₂O₃ which are constituents of PSZ contributes to thedeterioration of the material property. However, in the case where thebaking temperature is 1100° C., the difference is small and almostequivalent. However, in the case where the baking temperature is 940 °C. or lower, the difference will increase.

[0072] Further, it is seen that, comparing with the sample 19 which isunder the conventional conditions, this property is deteriorated in thecase where the agitating rate exceeds 6 m/s, the mixing amount of ZrO₂exceeds 0.22 wt %, and Y₂O₃ exceeds 0.012 wt %. An extremely excellentproperty may be obtained compared with the conventional one so long asthese areas are not exceeded. Further, the material may be baked at thetemperature 920° C., that is, lower than the melting point of Ag.However, even if exceeding the value and so long as the mixing quantityof ZrO₂ did not exceed 0.37 wt %, and the mixing quantity of Y₂O₃ doesnot exceed 0.021 wt % , the apparent density of 5 g/cm³ or more wasobtained at the baking temperature 920° C. as shown in the sample 8.

[0073] Agitating Rate

[0074] Samples where the apparent density 5.0 g/cm³ or more is securedby sintering at 920° C. or lower which is suited to the simultaneousbaking with Ag, are the samples 1 to 8, 12 to 15, 17 and 19. In the caseof the sample 9, the agitating rate is 10 m/s, and in this case, even ifthe average particle diameter and relative surface area are the same asthe samples 1 to 8, because the mixing amount of ZrO₂ and Y₂O₃ is toomuch, the apparent density 5.0 g/cm³ or more cannot be obtained in spiteof being at 940° C. Further, in the case of the sample 1, the agitatingrate is 1 m/s and since it takes 76 hours until the specific surfacearea comes to 8.0 m²/g, this is not desirable. Therefore, a preferredagitating rate is 2.0 to 8.0 m/s. TABLE 3 Measuring results of initialpermeability 870° 880° 910° 920° 940° 1000° 1100° C. C. C. C. C. C. C.Sample 1 351 592 981 1230 1695 2085 2120 Sample 2 365 602 1002 1245 17002093 2102 Sample 3 360 592 984 1235 1691 2100 2103 Sample 4 349 574 9501200 1650 2050 2100 Sample 5 349 574 910 1100 1550 2030 2099 Sample 6334 550 850 950 1400 1890 2100 Sample 7 280 450 700 850 1200 1600 2050Sample 8 202 350 631 780 1053 1450 2030 Sample 9 150 230 350 420 540 7001250 Sample 10 120 200 250 350 420 500 1230 Sample 11 160 230 360 430560 720 1300 Sample 12 360 600 1000 1250 1700 2100 2103 Sample 13 360570 1020 1300 1720 2100 2106 Sample 14 365 623 1020 1250 1720 2093 2150Sample 15 300 500 760 820 1150 1480 2050 Sample 16 140 180 240 320 400500 1260 Sample 17 340 550 900 1080 1530 2020 2100 Sample 18 98 142 202489 746 993 1300 Sample 19 350 525 910 1090 1550 2000 2130

[0075] Specific Surface Area

[0076] In the sample 11 where the specific surface area of the powder tobe obtained is 2.5 m²/g, and in the sample 16 of 3 m²/g, the apparentdensity of 5 g/cm³ or more cannot be obtained at 920° C. In the sample15 where the specific surface area is 6 m²/g, the apparent density of 5g/cm³ or more is obtained.

[0077] On the other hand, as the sample 12, if the specific surface areais 15 m²/g, the apparent density of 5 g/cm³ or more is obtained. In thesample 12, the crushing time is long as 93 hours. This may, however, beshortened by increasing the 5 agitating rate. TABLE 4 Measuring resultsof density of sintered materials 870° 880° 910° 920° 940° 1000° 1100° C.C. C. C. C. C. C. Sample 1 4.89 5.02 5.13 5.15 5.24 5.31 5.33 Sample 24.91 5.02 5.13 5.19 5.23 5.31 5.36 Sample 3 4.90 5.00 5.15 5.18 5.245.30 5.34 Sample 4 4.91 5.02 5.13 5.16 5.23 5.31 5.36 Sample 5 4.89 4.995.10 5.14 5.24 5.30 5.32 Sample 6 4.83 4.87 5.05 5.10 5.23 5.29 5.36Sample 7 4.80 4.85 5.00 5.05 5.18 5.29 5.34 Sample 8 4.79 4.85 4.98 5.035.15 5.27 5.32 Sample 9 4.25 4.34 4.46 4.62 4.80 4.99 5.32 Sample 103.90 4.00 4.25 4.35 4.50 4.85 5.20 Sample 11 4.20 4.35 4.50 4.60 4.805.00 5.33 Sample 12 4.89 5.00 5.12 5.13 5.24 5.30 5.33 Sample 13 4.905.03 5.15 5.16 5.24 5.31 5.32 Sample 14 4.92 5.02 5.15 5.16 5.24 5.325.35 Sample 15 4.89 5.00 5.16 5.18 5.26 5.30 5.35 Sample 16 3.85 4.054.40 4.55 4.75 4.95 5.32 Sample 17 4.83 4.95 5.06 5.13 5.24 5.30 5.35Sample 18 3.85 3.96 4.02 4.23 4.53 4.95 5.15 Sample 19 4.84 4.96 5.075.14 5.25 5.31 5.36

[0078] Ball Diameter

[0079] As to the samples 3, 14 to 16, the agitating rate and crushingtime were made constant, the ball diameter used as medium beads waschanged and the wet internal circulation media agitating mill was usedfor crushing. As seen in the samples 3, 14, and 15, the apparent density5 g/cm³ or more was obtained with the ball being within 0.2 to 5 mm indiameter by the sintering at 880° C. or higher

[0080] Baking Temperature

[0081] As seen in Table 4, in the samples 1 to 4, and 12 to 15, theapparent density 5 g/cm³ or more may be obtained if the bakingtemperature is 880° C. or higher. Further, in the case where the bakingtemperature is 940° C. or lower, which is the melting point of Ag, thesimultaneous baking with Ag is possible. Therefore, the bakingtemperature is 880 to 940° C, and preferably 880 to 920° C.

[0082] If the titania balls are used as in the sample 18, in order toobtain the density of the sintered material being 5 g/cm³, the bakingtemperature 1100° C. or higher is needed.

[0083] Comparison With the Method According to The Japanese Patent No.2708160

[0084] According to the method of the Japanese Patent No. 2708160, thecrushing is carried out, taking a long time as 196 hours in order tosuppress the mixing amount of ZrO₂ due to the abrasion of the mediumbeads to approximately 0.02 wt %. According to the invention, the mixingamounts of ZrO₂ and Y₂O₃ are increased more than 0.06 wt % and 0.003 wt% respectively as in the sample 2 within the area where the apparentdensity 5 g/cm³ or more may be obtained with baking at the temperatureof approximately 920° C. for the purpose of baking simultaneously withAg, thereby to make it possible to heighten the crushing efficiency byincreasing the agitating rate.

EXAMPLE 2

[0085] Now, a second example of the preferred embodiments is describedhereinafter.

[0086] Weighing and Crushing

[0087] The composition of NiO 8.7 mol %, CuO 10.0mol %, ZnO32.0 mol %,and Fe₂O₃ 49.3 mol % as the main constituent of Ni—Cu—Zn ferrite waswet-mixed with silicon nitride of 3 mm in diameter as medium beads bymeans of the media agitating mill of the wet internal circulation type,and was dried, followed by temporarily baking at 800 ° C. Subsequently,the temporarily baked material was pulverized by means of the mediaagitating mill of the wet internal circulation type by use of siliconnitride as medium beads and with the density of the temporarily basedmaterial being 33% as shown in Table5 in that the agitating rate,crushing time and ball diameter were varied as parameters as shown inthe left end column of Table 5.

[0088] Namely, as to the samples 20 to 28, the diameter of medium beadswas 3 mm, and, the agitating rates were varied as 1 m/s, 2.0 m/s, 4.0m/s, 4.3 m/s, 5.0 m/s, 6.0 m/s, 7.0 m/s, 8.0 m/s, and 10 m/s such thatthe average particle diameters of the materials were 0.5 μm, that is,the specific surface area were 8 m²/g, while in connection with therespective agitating rates, the crushing times were varied as 105 hours,92 hours, 62 hours, 53 hours, 46 hours, 32 hours, 23 hours, 14 hours,and 3 hours. Those were made the samples 20 to 28, in which all thepowders with particles of 0.5 μm in average diameter and with specificrelative surface area of 8 m²/g were obtained.

[0089] As to the samples 29 to 32, the diameter of the ball was 3 mm andthe agitating rate was 4 m/s while the crushing times were varied as 1.5hour, 2.1 hours, 128 hours, and 150 hours, and the powders of averageparticles being 2.0 μm, 1.5 μm, 0.3 μm, 0.2 μm, and the specific surfaceareas being 2 m²/g, 2.5 m²/g, 15 m²/g, and 17 m²/g were obtained.

[0090] As to the samples 33 to 35, the agitating rate was 4 m/s and thecrushing time was 62 hours constant while diameters of the balls werevaried as 0.2 mm, 5 mm, and 12 mm, and the powders of average particlesbeing 0.6 μm, 0.7 μm, and 1.4 μm, and relative surface areas being 7m²/g, 6 m²/g, and 3 m²/g were obtained respectively.

[0091] Further, for the purpose of comparison, the tests were carriedout as to the conventional samples 36 to 38. The samples 36 to 38 arethe same samples as the samples 17 to 19 in the first example,respectively. Therefore, the detailed descriptions are omitted.

[0092] Impurities and mixing amount thereof in the materials shown inTable 5 and the quantitative analysis of the main constituents afterproduction shown in Table 6 were measured by the same methods as ones inthe first example. The specific surface and the average particlediameter were also measured by the same methods as ones in the firstexample.

[0093] Production of Test Samples for Measuring Permeability and Densityof Sintered Materials

[0094] 10 wt parts of 3% water solvent of PVA124 was added as a binderto the materials shown in the samples 20 to 38 to make particles. Then,the materials were molded into predetermined shapes under the measuringconditions as later described and were baked for 2 hours in the air atthe temperatures 890° C., 900° C., 910° C., 920° C., 940° C., 1000° C.,and 1100° C. TABLE 5 Aver- age Crush- Ball Agita- Crush- grain speci-ing Ball diam- ting ing diam- fic Main impurities and ma- mater- eterrate time eter area mixing amounts (wt %) chine ials (mm) (m/s) (hr)(μm) (m²/g) Fe₃O₂ TiO₂ Al₂O₃ Si MoO₃ Crush- Sample 20 A* Silicon 3 1.0105 0.5 8 — — — 0.010 — ing nitride rate Sample 21 A Silicon 3 2.0 920.5 8 — — — 0.019 — nitride Sample 22 A Silicon 3 4.0 62 0.5 8 — — —0.033 — nitride Sample 23 A Silicon 3 4.3 53 0.5 8 — — — 0.037 — nitrideSample 24 A Silicon 3 5.0 46 0.5 8 — — — 0.042 — nitride Sample 25 ASilicon 3 6.0 32 0.5 8 — — — 0.056 — nitride Sample 26 A Silicon 3 7.023 0.5 8 — — — 0.082 — nitride Sample 27 A Silicon 3 8.0 14 0.5 8 — — —0.112 — nitride Sample 28 A Silicon 3 10.0 3 0.5 8 — — — 0.234 — nitrideCrush- Sample 29 A Silicon 3 4.0 1.5 2.0 2 — — — 0.014 — ing nitrideTime Sample 30 A Silicon 3 4.0 2.1 1.5 2.5 — — — 0.015 — nitride Sample31 A Silicon 3 4.0 128 0.3 15 — — — 0.058 — nitride Sample 32 A Silicon3 4.0 150 0.2 17 — — — 0.079 — nitride Ball Sample 33 A Silicon 0.2 4.062 0.6 7 — — — 0.033 — diam- nitride eter Sample 34 A Silicon 5 4.0 620.7 6 — — — 0.042 — nitride Sample 35 A Silicon 12 4.0 62 1.4 3 — — —0.239 — nitride Con- Sample 36 A Stainless 3 5.0 20 0.5 8 8.12 — — 0.0070.002 ven- steel tional Sample 37 A Titania 3 5.0 38 0.5 8 — 0.88 0.220.029 0.003 exam- Sample 38 B* Stainless 3 192 0.3 12 8.63 — — 0.0090.004 ple steel

[0095] TABLE 6 Weighed quality values and change of composition afterproduction Weighed quality Completion Fe₂O ZnO NiO CuO Fe₂O ZnO NiO CuOSample 20 49.3 32.0 8.7 10.0 49.28 32.05 8.72 9.95 Sample 21 49.3 32.08.7 10.0 49.26 32.05 8.75 9.94 Sample 22 49.3 32.0 8.7 10.0 49.27 32.038.74 9.96 Sample 23 49.3 32.0 8.7 10.0 49.23 32.06 8.75 9.96 Sample 2449.3 32.0 8.7 10.0 49.25 32.03 8.77 9.95 Sample 25 49.3 32.0 8.7 10.049.24 32.04 8.73 9.99 Sample 26 49.3 32.0 8.7 10.0 49.28 32.05 8.76 9.91Sample 27 49.3 32.0 8.7 10.0 49.23 32.07 8.74 9.96 Sample 28 49.3 32.08.7 10.0 49.28 32.06 8.73 9.93 Sample 29 49.3 32.0 8.7 10.0 49.24 32.068.76 9.94 Sample 30 49.3 32.0 8.7 10.0 49.21 32.03 8.78 9.98 Sample 3149.3 32.0 8.7 10.0 49.29 32.08 8.71 9.92 Sample 32 49.3 32.0 8.7 10.049.27 32.04 8.76 9.93 Sample 33 49.3 32.0 8.7 10.0 49.25 32.04 8.77 9.94Sample 34 49.3 32.0 8.7 10.0 49.24 32.07 8.72 9.97 Sample 35 49.3 32.08.7 10.0 49.26 32.05 8.78 9.91 Sample 36 46.0 34.0 9.5 10.5 49.02 32.108.97 9.91 Sample 37 49.3 32.0 8.7 10.0 49.34 31.90 8.73 9.92 Sample 3846.0 34.0 9.5 10.5 49.20 31.99 8.94 9.88

[0096] Evaluation

[0097] The core materials were evaluated with respect to the crushingtime until desired relative surface area were obtained, the confirmationof impurities which might be considered to have been mixed due toabrasion of the medium beads, the divergence in the composition of themain constituents of Fe₂O₃ZnO, CuO, and NiO, the initial permeabilityshown in Table 7, and the apparent densities shown in Table 8. Theinitial permeability was measured by the same method as in the firstexample.

[0098] With respect to the apparent density, the same calculation methodwas employed, and the apparent density was used for evaluating thesintered condition of the sintered material as in the first example.

[0099] Results of Evaluation

[0100] Mix of Impurities

[0101] In the case where a desired specific surface area is 8 m²/g as insamples 20 to 28 in Table 5, the crushing time is shortened as theagitating rate increases. It is, therefore, understood that theagitating rate is increased to heighten the crushing efficiency.However, the increasing of the agitating rate increases the abrasionamount of the medium beads. As to silicon nitride, the main constituentsSi are mixed into the material, but mixture of other constituents is notrecognized.

[0102] On the other hand, as to the samples 36 and 37 of theconventional examples, when comparing with the sample 24 of the sameball diameter and agitating rate with respect to the pulverizing timeand the abrasion amount of the balls, in the case of the sample 36,namely in the case of the stainless steel, the crushing time isshortened more than the case of silicon nitride and the crushingefficiency is very high, but the abrasion quantity is very much as about193 times of silicon nitride. The sample 37, namely the case of titania,the abrasion amount is 16.6 times of silicon nitride.

[0103] Divergence in the Composition Due to Mixed Impurities

[0104] Table 6 shows the divergences of the composition of the materialfrom weighing Fe₂O₃, ZnO, CuO, and NiO as the main constituents, thematerials having been mixed, crushed, temporarily baked and pulverized.These are the results of the quantitative analysis of the respectiveoxides. As is seen in Table 6, in the case where the stainless steel isused for medium beads as the samples 36 and 38, the divergence of Fe₂O₃is remarkable from weighing to completion, and in Ni—Cu—Zn ferrite, thecomposition of Fe₂O₃ which requires a most serious control, increases by3 mol % or higher from the weighing to the completion. Further since thestainless steel is different in hardness as to the outer part and innerpart, the medium beads used for a long time will cause a difference inthe mixed amount of Fe₂O₃. This indicates the difficulty of thecomposition control. TABLE 7 Measuring results of initial permeability890° 900° 910° 920° 940° 1000° 1100° C. C. C. C. C. C. C. Sample 20 450746 875 1090 1410 1990 2130 Sample 21 455 755 885 1090 1430 2000 2140Sample 22 452 749 878 1060 1410 2010 2140 Sample 23 437 724 849 10401370 1960 2120 Sample 24 414 686 805 962 1300 1940 2080 Sample 25 392649 761 831 1170 1810 2060 Sample 26 320 534 626 747 1020 1530 2020Sample 27 294 479 562 682 893 1370 1990 Sample 28 153 270 316 374 451662 1180 Sample 29 115 198 223 305 378 477 1150 Sample 30 163 271 320377 495 688 1120 Sample 31 460 760 892 1080 1420 2010 2110 Sample 32 469776 910 1110 1460 2030 2090 Sample 33 466 772 906 1090 1420 2000 2070Sample 34 348 574 673 903 1150 1810 1980 Sample 35 171 260 305 409 567887 1190 Sample 36 653 780 900 1080 1530 2020 2100 Sample 37 160 181 202489 746 993 1300 Sample 38 667 785 910 1090 1550 2000 2130

[0105] Relation Between Crushing Time and Relative Surface Area

[0106] Further as is understood from the samples 29 to 32, the specificsurface area is increased by prolonging the crushing time.

[0107] Relation Between Diameters of Balls and Relative Surface AreaFurther as shown in the samples 22, 33, 34 and 35 wherein the agitatingrate and crushing time are constant, in the case of the same agitatingrate and the same pulverizing time, the surface area of the powder wherethe ball diameter is 3 mm is largest and the crushing efficiency ishigh. If a ball mill is used as in the sample 38, the specific surfacearea is able to be 12 m²/g with the crushing for a long time as 192hours. However, this requires a crushing time about 1.5 times of thesample 31 where the wet internal circulation media agitating mill isoperated at the agitating rate 4 m/s. Moreover, in the case of thesample 38, it can be seen that the specific surface area is small andthe crushing efficiency of the ball mill is low.

[0108] Initial Permeability and Apparent Density

[0109] It can be seen that the permeability shown in Table 7 is inrelation to the apparent densities shown in Table 8. Namely, in thesamples 28 to 30, 35, and 37 where the permeability is relatively low,the apparent density is also low. In the samples 20 to 28, siliconnitride ball of 3 mm in diameter was used as the medium beads and thewet internal circulation media agitating mill was operated to vary theagitating rate for obtaining the specific surface area 8 m²/g, but bothof the permeability and the density of the sintered material weredeteriorated when the agitating rate was heightened. This is because theincrease of mixing amount of Si by abrasion of silicon nitridecontributes to the deterioration of the material property. However, inthe case where the baking temperature is 1100° C., the difference issmall and almost equivalent. However, in the case where the bakingtemperature is 940° C. or lower, the difference will increase.

[0110] Further, it is seen that, comparing with the sample 38 which isunder the conventional conditions, this property is deteriorated in thecase where the agitating rate exceeds 6 m/s and the mixing amount of Siexceeds 0.056 wt %. An extremely excellent property may be obtainedcompared with the conventional one so long as these areas are notexceeded. Further, the material may be baked at the temperature 920° C.,that is, lower than the melting point of Ag. However, even if theagitating rate exceeds 6 m/s, so long as the mixing quantity of Si didnot exceed 0.112 wt %, the apparent density of 5 g/cm³ or more wasobtained at the baking temperature 920° C. as shown in the sample 27.TABLE 8 Measuring results of density of sintered materials 890° 900°910° 920° 940° 1000° 1100° C. C. C. C. C. C. C. Sample 20 4.75 4.88 5.105.14 5.25 5.30 5.33 Sample 21 4.77 4.90 5.09 5.14 5.23 5.30 5.32 Sample22 4.74 4.89 5.09 5.14 5.24 5.28 5.34 Sample 23 4.75 4.87 5.08 5.13 5.235.28 5.31 Sample 24 4.73 4.84 5.07 5.12 5.24 5.28 5.32 Sample 25 4.654.77 5.03 5.09 5.22 5.29 5.30 Sample 26 4.64 4.75 5.00 5.04 5.21 5.275.31 Sample 27 4.63 4.76 4.96 5.01 5.14 5.28 5.30 Sample 28 4.00 4.114.42 4.60 4.78 4.98 5.30 Sample 29 3.65 3.84 4.20 4.30 4.47 4.84 5.21Sample 30 3.67 3.86 4.44 4.55 4.58 4.99 5.20 Sample 31 4.74 4.88 5.095.13 5.24 5.28 5.35 Sample 32 4.73 4.88 5.09 5.14 5.23 5.28 5.34 Sample33 4.77 4.90 5.10 5.15 5.24 5.30 5.32 Sample 34 4.70 4.85 5.04 5.12 5.205.28 5.33 Sample 35 3.66 3.82 4.37 4.50 4.72 4.93 5.30 Sample 36 4.985.03 5.06 5.13 5.24 5.30 5.35 Sample 37 3.97 3.99 4.02 4.23 4.53 4.955.15 Sample 38 4.99 5.03 5.07 5.14 5.25 5.31 5.36

[0111] Agitating Rate

[0112] Samples where the apparent density 5.0 g/cm³ or more is securedby sintering at 920° C. or lower which is suited to the simultaneousbaking with Ag, are the samples 20 to 27, 31 to 34, 36 and 38. In thecase of the sample 28, the agitating rate is 10 m/s, and in this case,even if the average particle diameter and relative surface area are thesame as the samples 1 to 8, because the mixing amount of Si is too much,the apparent density 5.0 g/cm³ or more cannot be obtained in spite ofbeing at 940° C. Further, in the case of the sample 20, the agitatingrate is 1 m/s and since it takes 105 hours until the specific surfaceare a comes to8.0 m²/g, this is not desirable. Therefore, a preferredagitating rate is 2.0 to 8.0 m/s.

[0113] Specific Surface Area

[0114] In the sample 30 where the specific surface area of the powder tobe obtained is 2.5 m²/g, and in the sample 35 of 3 m²/g, the apparentdensity of 5 g/cm³ or more cannot be obtained at 920° C. In the sample34 where the specific surface area is 6 m²/g, the apparent density of 5g/cm³ or more is obtained.

[0115] On the other hand, as the sample 31, if the specific surface areais 15 m²/g, the apparent density of 5 g/cm³ or more is obtained. In thesample 12, the crushing time is long as 93 hours. This may, however, beshortened by increasing the agitating rate.

[0116] Ball Diameter

[0117] As to the samples 22, 33 to 35, the agitating rate and crushingtime were made constant, the ball diameter used as medium beads waschanged and the wet internal circulation media agitating mill was usedfor crushing. As seen in the samples 22, 33, and 34, the apparentdensity 5 g/cm³ or more was obtained with the ball being within 0.2 to 5mm in diameter by the sintering at 910° C. or higher

[0118] Baking Temperature

[0119] As seen in Table 8, the apparent density 5 g/cm³ or more may beobtained if the baking temperature is 910° C. or higher. Further, in thecase where the baking temperature is 940° C. or lower, which is lowerthan 960° C. of the melting point of Ag, the simultaneous baking with Agis possible. Therefore, the baking temperature is 910 to 940° C., andpreferably 910 to 920° C.

[0120] If the titania balls are used as in the sample 37, in order toobtain the density of the sintered material being 5 g/cm³, the bakingtemperature 1100° C. or higher is needed.

[0121] Comparison With the Method According to the Japanese Patent No.2708160

[0122] According to the method of the Japanese Patent No. 2708160, thecrushing is carried out, taking a long time as 196 hours in order tosuppress the mixing amount of ZrO₂ due to the abrasion of the mediumbeads to approximately 0.02 wt %. According to the invention, by meansof the media agitating mill of the wet internal circulation type and byusing silicon nitride as medium beads, the mixing amounts of abrasionpowder are increased more than 0.010 wt % respectively as in the sample21 within the area where the apparent density 5 g/cm³ or more may beobtained with baking at the temperature of approximately 920° C. for thepurpose of baking simultaneously with Ag, thereby to make it possible toheighten the crushing efficiency by increasing the agitating rate.

EXAMPLE 3

[0123] Now, a third example of the preferred embodiments is describedhereinafter.

[0124] Weighing and Crushing

[0125] The composition of NiO 8.7 mol %, CuO 10.0 mol %, ZnO 32.0 mol %,and Fe₂O₃ 49.3 mol % as the main constituent of Ni—Cu—Zn ferrite waswet-mixed with partially stabilized zirconia (PSZ) and silicon nitrideof 3 mm in diameter as medium beads by means of the media agitating millof the wet internal circulation type, and was dried, followed bytemporarily baking at 800° C. Subsequently, the temporarily bakedmaterial was pulverized by means of the media agitating mill of the wetinternal circulation type by use of partially stabilized zirconia (PSZ)and silicon nitride as medium beads and with the density of thetemporarily based material being 33% as shown in Table 9 in that theagitating rate, crushing time and ball diameter were varied asparameters as shown in the left end column of Table 9.

[0126] Namely, as to the samples 39 to 47, the ratio of medium beads was(PSZ):(silicon nitride)=50%: 50% as the volume ratio, and the diameterof medium beads was 3 mm, and, the agitating rates were varied as 1 m/s,2.0 m/s, 4.0 m/s, 4.3 m/s, 5.0 m/s, 6.0 m/s, 7.0 m/s, 8.0 m/s, and 10m/s such that the average particle diameters of the materials were 0.5μm, that is, the specific surface area were 8 m²/g, while in connectionwith the respective agitating rates, the crushing times were varied as93 hours, 82 hours, 55 hours, 45 hours, 40 hours, 28 hours,. 20 hours,12 hours, and 2.5 hours. Those were made the samples 39 to 47, in whichall the powders with particles of 0.5 μm in average diameter and withspecific relative surface area of 8 m²/g were obtained.

[0127] As to the samples 48 to 51, the diameter of the ball was 3 mm andthe agitating rate was 4 m/s while the crushing times were varied as 1hour, 1.5 hours, 115 hours, and 134 hours, and the powders of averageparticles being 2.0 μm, 1.5 μm, 0.3 μm, 0.2 μm, and the specific surfaceareas being 2 m²/g, 2.5 m²/g, 15 m²/g, and 17 m²/g were obtained.

[0128] As to the samples 52 to 54, the agitating rate was 4 m/s and thecrushing time was 55 hours constant while diameters of the balls werevaried as 0.2 mm, 5 mm, and 12 mm, and the powders of average particlesbeing 0.6 μm, 0.7 μm, and 1.5 μm, and relative surface areas being 7m²/g, 6 m²/g, and 3 m²/g were obtained respectively.

[0129] As to the samples 55 to 57, the agitating rate of 4 m/s, and thecrushing times of 55 hour, and the ball diameter of 3 mm were madeconstant. The ratio of PSZ and silicon nitride, which are used as mediumbeads, was varied as (PSZ):(Silicon nitride)=20:80, (PSZ):(Siliconnitride)=80:20, and (PSZ):(Silicon nitride)=99:1, respectively in volumeratio. The powders of average particles of 0.7 μm, 0.45 μm, and 0.45 μm,and the specific surface areas of 6 m²/g, 9 m²/g, 9 m²/g wererespectively obtained.

[0130] Further, for the purpose of comparison, the tests were carriedout as to the conventional samples 58 to 60. The samples 58 to 60 arethe same samples as the samples 17 to 19 in the first example,respectively. Therefore, the detailed descriptions are omitted.

[0131] Impurities and mixing amount thereof in the materials shown inTable 10 and the quantitative analysis of the main constituents afterproduction shown in Table 11 were measured by the same methods as onesin the first example. The specific surface and the average particlediameter were also measured by the same methods as ones in the firstexample.

[0132] Production of Test Samples for Measuring Permeability and Densityof Sintered Materials

[0133] 10 wt parts of 3% water solvent of PVA124 was added as a binderto the materials shown in the samples 39 to 60 to make particles. Then,the materials were molded into predetermined shapes under the measuringconditions as later described and were baked for 2 hours in the air atthe temperatures 870° C., 880° C., 910° C., 920° C., 940° C., 1100° C.,and 1100° C.

[0134] Evaluation

[0135] The core materials were evaluated with respect to the crushingtime until desired relative surface area were obtained, the confirmationof impurities which might be considered to have been mixed due toabrasion of the medium beads, the divergence in the composition of themain constituents of Fe₂O₃ZnO, CuO, and NiO, the initial permeabilityshown in Table 12, and the apparent densities shown in Table 13. Theinitial permeability was measured by the same method as in the firstexample.

[0136] With respect to the apparent density, the same calculation methodwas employed, and the apparent density was used for evaluating thesintered condition of the sintered material as in the first example.TABLE 9 Sail Agitating Crushing Average grain Specific Crushing Balldiameter rate time diameter area machine materials (mm) (m/s) (hr) (μm)(m²/g) Crushing Sample 39 A* PSZ:Silicon nitride = 50:50 3 1 93 0.5 8rate Sample 40 A PSZ:Silicon nitride = 50:50 3 2 82 0.5 8 Sample 41 APSZ:Silicon nitride = 50:50 3 4 55 0.5 8 Sample 42 A PSZ:Silicon nitride= 50:50 3 4.3 45 0.5 8 Sample 43 A PSZ:Silicon nitride = 50:50 3 5 400.5 8 Sample 44 A PSZ:Silicon nitride = 50:50 3 6 28 0.5 8 Sample 45 APSZ:Silicon nitride = 50:50 3 7 20 0.5 8 Sample 46 A PSZ:Silicon nitride= 50:50 3 8 12 0.5 8 Sample 47 A PSZ:Silicon nitride = 50:50 3 10 2.50.5 8 Crushing Sample 48 A PSZ:Silicon nitride = 50:50 3 4 1 2.2 1.8Time Sample 49 A PSZ:Silicon nitride = 50:50 3 4 1.5 1.8 2.2 Sample 50 APSZ:Silicon nitride = 50:50 3 4 115 0.3 15 Sample 51 A PSZ:Siliconnitride = 50:50 3 4 134 0.2 17 Ball Sample 52 A PSZ:Silicon nitride =50:50 0.2 4 55 0.6 7 diameter Sample 53 A PSZ:Silicon nitride = 50:50 54 55 0.7 6 Sample 54 A PSZ:Silicon nitride = 50:50 12 4 55 1.5 3 RatioSample 55 A PSZ:Silicon nitride = 20:80 3 4 55 0.7 6 Sample 56 APSZ:Silicon nitride = 80:20 3 4 55 0.45 9 Sample 57 A PSZ:Siliconnitride = 99:1  3 4 55 0.45 9 Conventional Sample 58 A Stainless steel 35 20 0.5 8 example Sample 59 A Titania 3 5 38 0.5 8 Sample 60 B*Stainless steel 3 192 0.3 12

[0137] TABLE 10 Main impurities and mixing amounts (wt %) ZrO₂ Y₂O₃Fe₂O₃ TiO₂ Al₂O₃ Si MoO₃ Crushing rate Sample 39 0.005 0.001 — — — 0.006— Sample 40 0.031 0.001 — — — 0.010 — Sample 41 0.062 0.004 — — — 0.015— Sample 42 0.071 0.004 — — — 0.018 — Samole 43 0.092 0.005 — — — 0.021— Sample 44 0.111 0.006 — — — 0.027 — Sample 45 0.153 0.008 — — — 0.041— Sample 46 0.194 0.011 — — — 0.056 — Sample 47 0.302 0.015 — — — 0.112— Crushing Time Sample 48 0.010 0.001 — — — 0.007 — Sample 49 0.0120.001 — — — 0.007 — Sample 50 0.120 0.006 — — — 0.028 — Sample 51 0.1400.009 — — — 0.039 — Ball diameter Sample 52 0.05 0.003 — — — 0.014 —Sample 53 0.09 0.005 — — — 0.020 — Sample 54 0.32 0.017 — — — 0.117 —Ratio Sample 55 0.03 0.001 — — — 0.038 — Sample 56 0.10 0.006 — — —0.001 — Sample 57 0.12 0.007 — — — 0.001 — Conventional example Sample58 — — 8.12 — — 0.007 0.002 Sample 59 — — — 0.88 0.22 0.029 0.003 Sample60 8.63 — — 0.009 0.004

[0138] Results of Evaluation

[0139] [Mix of Impurities]

[0140] In the case where a desired specific surface area is 8 m²/g as insamples 39 to 47 in Table 9, the crushing time is shortened as theagitating rate increases. It is, therefore, understood that theagitating rate is increased to heighten the crushing efficiency.However, the increasing of the agitating rate increases the abrasionamount of the medium beads. As shown in FIG. 10, as to PSZ and siliconnitride, the main constituents ZrO₂ , Y₂O₃, and Si are mixed into thematerial, but mixture of other constituents is not recognized.

[0141] On the other hand, as to the samples 58 and 59 of theconventional examples, when comparing with the sample 43 of the sameball diameter and agitating rate with respect to the pulverizing timeand the abrasion amount of the balls, in the case of the sample 58,namely in the case of the stainless steel, the crushing time isshortened more than the case of (PSZ):(Silicon nitride)=50:50 and thecrushing efficiency is very high, but the abrasion quantity is very muchas about 73 times of (PSZ):(Silicon nitride)=50:50. The sample 59,namely the case of titania, the abrasion amount is about 73 times of(PSZ):(Silicon nitride)=50:50.

[0142] Divergence in the Composition Due to Mixed Impurities

[0143] Table 11 shows the divergences of the composition of the materialfrom weighing Fe₂O₃, ZnO, CuO, and NiO as the main constituents, thematerials having been mixed, crushed, temporarily baked and pulverized.These are the results of the quantitative analysis of the respectiveoxides. As is seen in Table 11, in the case where the stainless steel isused for medium beads as the samples 58 and 60, the divergence of Fe₂O₃is remarkable from weighing to completion, and in Ni—Cu—Zn ferrite, thecomposition of Fe₂O₃ which requires a most serious control, increases by3 mol % or higher from the weighing to the completion. Further since thestainless steel is different in hardness as to the outer part and innerpart, the medium beads used for a long time will cause a difference inthe mixed amount of Fe₂O₃. This indicates the difficulty of thecomposition control.

[0144] Relation Between Crushing Time and Relative Surface Area

[0145] Further as is understood from the samples 48 to 51, the specificsurface area is increased by prolonging the crushing time. TABLE 11Weighed quality values and change of composition after productionWeighed quality Completion Fe₂O₃ ZnO NiO CuO Fe₂O₃ ZnO NiO CuO Sample 3949.3 32.0 8.7 10.0 49.20 32.05 8.77 9.98 Sample 40 49.3 32.0 8.7 10.049.21 32.03 8.84 9.92 Sample 41 49.3 32.0 8.7 10.0 49.20 32.05 8.83 9.92Sample 42 49.3 32.0 8.7 10.0 49.21 32.03 8.81 9.95 Sample 43 49.3 32.08.7 10.0 49.25 32.08 8.71 9.96 Sample 44 49.3 32.0 8.7 10.0 49.22 32.068.80 9.92 Sample 45 49.3 32.0 8.7 10.0 49.23 32.05 8.74 9.98 Sample 4649.3 32.0 8.7 10.0 49.25 32.04 8.75 9.96 Sample 47 49.3 32.0 8.7 10.049.25 32.03 8.77 9.95 Sample 48 49.3 32.0 8.7 10.0 49.26 32.06 8.72 9.96Sample 49 49.3 32.0 8.7 10.0 49.23 32.05 8.80 9.92 Sample 50 49.3 32.08.7 10.0 49.25 32.00 8.82 9.93 Sample 51 49.3 32.0 8.7 10.0 49.22 32.028.82 9.94 Sample 52 49.3 32.0 8.7 10.0 49.25 32.05 8.72 9.98 Sample 5349.3 32.0 8.7 10.0 49.22 32.02 8.77 9.99 Sample 54 49.3 32.0 8.7 10.049.26 32.01 8.81 9.92 Sample 55 49.3 32.0 8.7 10.5 49.25 32.05 8.72 9.98Sample 56 49.3 32.0 8.7 10.0 49.25 32.06 8.73 9.96 Sample 57 49.3 32.08.7 10.0 49.25 32.04 8.73 9.98 Sample 58 46.0 34.0 9.5 10.5 49.02 32.108.97 9.91 Sample 59 49.3 32.0 8.7 10.0 49.34 31.90 8.73 9.92 Sample 6046.0 34.0 9.5 10.5 49.20 31.99 8.94 9.88

[0146] Relation Between Diameters of Balls and Relative Surface Area

[0147] Further as shown in the samples 41, 52, 53 and 54 wherein theagitating rate and crushing time are constant, in the case of the sameagitating rate and the same pulverizing time, the surface area of thepowder where the ball diameter is 3 mm is largest and the crushingefficiency is high. If a ball mill is used as in the sample 60, thespecific surface area is able to be 12 m²/g with the crushing for a longtime as 192 hours. However, this requires a crushing time more thantwice of the sample 50 where the wet internal circulation mediaagitating mill is operated at the agitating rate 4 m/s. Moreover, in thecase of the sample 60, it can be seen that the specific surface area issmall and the crushing efficiency of the ball mill is low.

[0148] Initial Permeability and Apparent Density

[0149] It can be seen that the permeability shown in Table 12 is inrelation to the apparent densities shown in Table 13. Namely, in thesamples 47 to 49, 54, and 59 where the permeability is relatively low,the apparent density is also low. In the samples 39 to 47, PSZ andsilicon nitride balls of 3 mm in diameter were used as the medium beadsand the wet internal circulation media agitating mill was operated tovary the agitating rate for obtaining the specific surface area 8 m²/g,but both of the permeability and the density of the sintered materialwere deteriorated when the agitating rate was heightened. This isbecause the increase of mixing amount of ZrO₂ and Y₂O₃ which areconstituents of PSZ and mixing amount of Si by the silicon nitridecontributes to the deterioration of the material property. However, inthe case where the baking temperature is 1100° C., the difference issmall and almost equivalent. However, in the case where the bakingtemperature is 940° C. or lower, the difference will increase.

[0150] Further, it is seen that, comparing with the sample 60 which isunder the conventional conditions, this property is deteriorated in thecase where the agitating rate exceeds 6 m/s, the mixing amount of ZrO₂exceeds 0.111 wt %, Y₂O₃ exceeds 0.006 wt %, and Si exceeds 0.027 wt %.An extremely excellent property may be obtained compared with theconventional one so long as these areas are not exceeded. Further, thematerial may be baked at the temperature 920° C., that is, lower thanthe melting point of Ag. However, even if exceeding the value and solong as the mixing quantity of ZrO₂ did not exceed 0.194 wt %, and themixing quantity of Y₂O₃ does not exceed 0.011 wt %, and the mixingquantity of Si does not exceed 0.056 wt %, the apparent density of 5g/cm³ or more was obtained at the baking temperature 920° C. as shown inthe sample 46.

[0151] Agitating Rate

[0152] Samples where the apparent density 5.0 g/cm³ or more is securedby sintering at 920° C. or lower which is suited to the simultaneousbaking with Ag, are the samples 39 to 46, 50 to 53, 55 to 57, 58 and 60.In the case of the sample 47, the agitating rate is 10 m/s, and in thiscase, even if the average particle diameter and relative surface areaare the same as the samples 39 to 46, because the mixing amount of ZrO₂,Y₂O₃, and Si is too much, the apparent density 5.0 g/cm³ or more cannotbe obtained in spite of being at 940° C. Further, in the case of thesample 39, the agitating rate is 1 m/s and since it takes 93 hours untilthe specific surface area comes to 8.0 m²/g, this is not desirable.Therefore, a preferred agitating rate is 2.0 to 8.0 m/s. TABLE 12Measuring results of initial permeability 870° 880° 910° 920° 940° 1000°1100° C. C. C. C. C. C. C. Sample 39 330 520 931 1200 1680 2056 2092Sample 40 345 523 963 1210 1683 2082 2102 Sample 41 340 519 932 12061679 2085 2105 Sample 42 329 480 925 1165 1615 1980 2102 Sample 43 326476 893 1098 1515 1907 2052 Sample 44 303 454 823 939 1325 1825 2036Sample 45 255 383 658 846 1138 1605 1996 Sample 46 180 303 592 753 9831435 1983 Sample 47 126 203 293 386 496 653 1246 Sample 48 108 186 232336 403 485 1180 Sample 49 153 207 302 393 515 692 1253 Sample 50 342527 971 1220 1695 2092 2106 Sample 51 346 516 968 1232 1701 2100 2102Sample 52 347 529 982 1231 1698 2096 2136 Sample 53 372 405 672 903 12301632 2115 Sample 54 122 192 228 343 410 495 1243 Sample 55 322 463 8631068 1493 1876 2023 Sample 56 352 583 974 1223 1685 2092 2110 Sample 57358 590 980 1232 1692 2098 2125 Sample 58 340 550 900 1080 1530 20202100 Sample 59 98 142 202 489 746 993 1300 Sample 60 350 525 910 10901550 2000 2130

[0153] Specific Surface Area

[0154] In the sample 49 where the specific surface area of the powder tobe obtained is 2.5 m²/g, and in the sample 54 of 3 m²/g, the apparentdensity of 5 g/cm³ or more cannot be obtained at 920° C. In the sample53 where the specific surface area is 6 m²/g, the apparent density of5.0 g/cm³ or more is obtained.

[0155] On the other hand, as the sample 50, if the specific surface areais 15 m²/g, the apparent density of 5.0 g/cm³ or more is obtained. Inthe sample 50, the crushing time is long as 115 hours. This may,however, be shortened by increasing the agitating rate. TABLE 13Measuring results of density of sintered materials 870° 880° 910° 920°940° 1000° 1100° C. C. C. C. C. C. C. Sample 39 4.65 4.90 5.02 5.12 5.245.31 5.33 Sample 40 4.67 4.90 5.02 5.13 5.23 5.30 5.34 Sample 41 4.654.88 5.02 5.12 5.24 5.30 5.35 Sample 42 4.67 4.91 5.02 5.10 5.22 5.305.36 Sample 43 4.65 4.88 4.98 5.08 5.24 5.29 5.32 Sample 44 4.60 4.754.88 5.05 5.22 5.29 5.36 Sample 45 4.55 4.73 4.85 5.02 5.20 5.28 5.34Sample 46 4.54 4.70 4.84 5.00 5.15 5.27 5.32 Sample 47 4.15 4.25 4.354.52 4.70 5.00 5.32 Sample 48 3.88 4.00 4.22 4.36 4.50 4.82 5.15 Sample49 4.10 4.20 4.30 4.55 4.68 4.99 5.30 Sample 50 4.67 4.93 5.00 5.10 5.225.30 5.32 Sample 51 4.68 4.92 5.00 5.09 5.24 5.30 5.32 Sample 52 4.684.93 5.03 5.10 5.25 5.31 5.35 Sample 53 4.65 4.89 5.06 5.12 5.25 5.305.33 Sample 54 3.80 4.02 4.20 4.30 4.48 4.80 5.10 Sample 55 4.63 4.835.00 5.07 5.22 5.25 5.32 Sample 56 4.82 4.96 5.10 5.17 5.24 5.32 5.35Sample 57 4.90 5.00 5.15 5.18 5.24 5.33 5.36 Sample 58 4.83 4.95 5.065.13 5.24 5.30 5.35 Sample 59 3.85 3.96 4.02 4.23 4.53 4.95 5.15 Sample60 4.84 4.96 5.07 5.14 5.25 5.31 5.36

[0156] Ball Diameter

[0157] As to the samples 41, 52 to 53, the agitating rate and crushingtime were made constant, the ball diameter used as medium beads waschanged and the wet internal circulation media agitating mill was usedfor crushing. As seen in the samples 41, 55, and 57, the apparentdensity 5 g/cm³ or more was obtained with the ball being within 0.2 to 5mm in diameter by the sintering at 920° C. or higher.

[0158] Ratio of PSZ Beads and Silicon Nitride Beads

[0159] As to the samples 41, 55 to 57, the ball diameter, agitatingrate, and crushing time were made constant, and The volume ratio of PSZand silicon nitride, which are used as medium beads, was changed withusing the wet internal circulation media agitating mill for crushing. Asseen in the samples, the apparent density 5 g/cm³ or more was obtainedby the sintering at 920° C. or higher in the range between(PSZ):(Silicon nitride)=20:80 and 99:1.

[0160] Baking Temperature

[0161] In the case where the baking temperature is 940° C. or lower,which is lower than 960° C. of the melting point of Ag, the simultaneousbaking with Ag is possible. Therefore, the baking temperature is 880 to940° C., and preferably 910 to 920° C.

[0162] If the titania balls are used as in the sample 59, in order toobtain the density of the sintered material being 5 g/cm³, the bakingtemperature 1100° C. or higher is needed.

[0163] Comparison With the Method According to the Japanese Patent No.2708160

[0164] According to the method of the Japanese Patent No. 2708160, thecrushing is carried out, taking a long time as 196 hours in order tosuppress the mixing amount of ZrO₂ due to the abrasion of the mediumbeads to approximately 0.02 wt %. According to the invention, the mixingamounts of ZrO₂ and Y₂O₃ are increased more than 0.03 wt % and 0.001 wt% respectively as in the sample 45, and the mixing amount of Si isfurther increased more than 0.001 wt % with using silicon nitride beadsat the same time as in the sample 56 within the area where the apparentdensity 5 g/cm³ or more may be obtained with baking at the temperatureof approximately 920° C. for the purpose of baking simultaneously withAg, thereby to make it possible to heighten the crushing efficiency byincreasing the agitating rate.

[0165] According to the oxide magnetic material according to the presentinvention, PSZ is used to contain the above- mentioned amounts of Y₂O₃and ZrO₂ in Ni—Cu—Zn, thereby to make it possible to bake the materialat the temperature for baking simultaneously with Ag and to obtain asintered material of the apparent density being 5 g/cm³ or more bysintering and of permeability which may satisfy demands. Further withthe above-mentioned range of amounts of Y₂O₃ and ZrO₂ beingpredetermined, the oxide magnetic material may be obtained in ashortened period of time, and the production cost may be lowered.

[0166] Similar effect is accomplished by using silicon nitride insteadof PSZ in order to contain the above-mentioned amounts of Si inNi—Cu—Zn. In this case, with the above-mentioned range of amounts of Sibeing predetermined, the oxide magnetic material may be obtained in ashortened period of time, and the production cost may be lowered.

[0167] Furthermore, similar effect is accomplished by using both PSZ andsilicon nitride instead of PSZ in order to contain the above-mentionedamounts of Y₂O₃ZrO₂, and Si in Ni—Cu—Zn. In this case, with theabove-mentioned range of amounts of Y₂O₃, ZrO₂, and Si beingpredetermined, the oxide magnetic material maybe obtained in a shortenedperiod of time, and the production cost may be lowered.

[0168] The chip parts according to the second and third aspect of theinvention are formed as the bulk-type coil part or the laminated coilpart by using the sintered one of the oxide magnetic material accordingto the first aspect. Therefore, the thus obtained coil parts may copewith the ones as baked at high temperature with respect to strength andpermeability.

[0169] The chip part according to the fourth aspect of the invention hasthe internal conductor containing as the main constituent Ag or thealloy of Ag and Pd according to the third aspect. Therefore, such a coilpart of high Q may be obtained.

[0170] According to the method in the fifth aspect of the invention forproducing the oxide magnetic material, the balls of partially stabilizedzirconia are used to crush the material after being temporarily baked,thereby to eliminate the difficult problem in the composition control asin the case that the conventional stainless balls are used. Further,since Y₂O₃ and ZrO₂ are mixed into the material by utilizing thecrushing process, the processes for weighing and mixing may be no longernecessary. Further, the agitating rate is increased to shorten thecrushing period of time, thereby to lower the production cost incontrast to the case for suppressing the mixing quantity of ZrO₂ asdescribed in the Japanese Patent No. 2708160.

[0171] Similar effect is accomplished by using silicon nitride ballsinstead of PSZ balls. In this case, since Si is mixed into the materialby utilizing the crushing process, the processes for weighing and mixingmay be no longer necessary.

[0172] Furthermore, similar effect is accomplished by using both PSZballs and silicon nitride balls. In this case, since, Y₂O₃ and ZrO₂ andSi is mixed into the material by utilizing the crushing process, theprocesses for weighing and mixing may be no longer necessary.

[0173] According to the methods as in the sixth or eighth aspect of theinvention for producing the oxide magnetic material, since diameter ofthe medium beads, agitating rate of the medium beads, specific area ofcrushed material after temporary baking are adjusted in theabove-described range for use, the oxide magnetic material can beobtained without lowering the crushing efficiency or invitingdeterioration of the density and permeability of the sintered material.

[0174] According to the method as in the ninth aspect of the inventionfor producing the chip part, since the magnetic material of the oxidemagnetic material crushed by the medium beads and the internal conductorare molded and baked in the above-described range, insufficientsintering, diffusion of the electrode material in ferrite may beprevented. Therefore, the deterioration of electro-magnetic property isprevented.

[0175] While only certain embodiments of the invention have beenspecifically described herein, it will be apparent that numerousmodifications may be made thereto without departing from the spirit andscope of the invention.

[0176] The present invention is based on Japanese Patent ApplicationsNo. Hei. 11-232412, Hei. 11-262934, and Hei. 11-262935 which isincorporated herein by reference.

What is claimed is:
 1. An oxide magnetic material comprising: mainconstituents including Fe₂O₃, ZnO, CuO and NiO, wherein Y₂O₃ of 0.003 to0.021 wt % and ZrO₂ of 0.06 to 0.37 wt % are included in said mainconstituents with respect 5 to all amounts.
 2. A chip part comprising: asintered material of an oxide magnetic material including mainconstituents having Fe₂O₃, ZnO, CuO and NiO, wherein Y₂O₃of 0.003 to0.021 wt % and ZrO₂ of 0.06 to 5 0.37 wt % are included in said mainconstituents with respect to all amounts.
 3. The chip according to claim2, wherein said chip part is formed as a bulk-type coil part.
 4. Thechip according to claim 2, wherein said chip part has an electricconductor layer in said sintered material, and said chip part at leastpartly includes a laminated coil part.
 5. The chip part according toclaim 4, wherein an internal conductor has one of Ag and an alloy of Agand Pd as a main constituent.
 6. An oxide magnetic material comprising:main constituents including Fe₂O₃ZnO, CuO and NiO, wherein Si of 0.010to 0.0112 wt % is included in said main constituents with respect to allamounts.
 7. A chip part comprising: a sintered material of an oxidemagnetic material including main constituents having Fe₂O₃, ZnO, CuO andNiO, wherein Si of 0.010 to 0.0112 wt % is included in said mainconstituents with respect to all amounts.
 8. The chip according to claim7, wherein said chip part is formed as a bulk-type coil part.
 9. Thechip according to claim 7, wherein said chip part has an electricconductor layer in said sintered material, and said chip part at leastpartly includes a laminated coil part.
 10. The chip part according toclaim 9, wherein an internal conductor has one of Ag and an alloy of Agand Pd as a main constituent.
 11. An oxide magnetic material comprising:main constituents including Fe₂O₃, ZnO, CuO and NiO, wherein Y₂O₃of0.001to 0.011 wt %, ZrO₂ of0.031to0.194 wt %, and Si of 0.010 to 0.056wt % are included in said main constituents with respect to all amounts.12. A chip part comprising: a sintered material of an oxide magneticmaterial including main constituents having Fe₂O₃, ZnO, CuO and NiO,wherein Y₂O₃of 0.001 to 0.011 wt %, ZrO₂ of0.031 to 0.194 wt %, and Siof 0.010 to 0.056 wt % are included in said main constituents withrespect to all amounts.
 13. The chip according to claim 12, wherein saidchip part is formed as a bulk-type coil part.
 14. The chip according toclaim 12, wherein said chip part has an electric conductor layer in saidsintered material, and said chip part at least partly includes alaminated coil part.
 15. The chip part according to claim 14, wherein aninternal conductor has one of Ag and an alloy of Ag and Pd as a mainconstituent.
 16. A method for producing an oxide magnetic material, saidmethod comprising: mixing and crushing a raw material with a mediaagitating mill of a wet internal circulation type; temporarily bakingthe mixed and crushed material; and crushing the temporarily bakedmaterial with the media agitating mill; wherein a partly stabilizedzirconia is used as medium beads at the time of mixing and crushing theraw material and at the time of crushing the temporarily baked materialin order to cause Y₂O₃ of 0.003 to 0.021 wt % and ZrO₂ of 0.06 to 0.37wt % to contain therein with respect to all amounts in the oxidemagnetic material by wear of the medium beads.
 17. The method forproducing the oxide magnetic material according to claim 16, whereindiameter of the medium beads is in the range between 0.2 and 5 mm. 18.The method for producing the oxide magnetic material according to claim16, wherein agitating rate of the medium beads is in the range between2.0 and 8.0 m/s.
 19. The method for producing the oxide magneticmaterial according to claim 16, wherein the material is crushed aftertemporarily baked so that powders of specific surface area of 6.0 to15.0 m²/g are obtained.
 20. A method for producing a chip part, saidmethod comprising: producing an oxide magnetic material, including:mixing and crushing a raw material with a media agitating mill of a wetinternal circulation type; temporarily baking the mixed and crushedmaterial; and crushing the temporarily baked material with the mediaagitating mill, wherein a partly stabilized zirconia is used as mediumbeads at the time of mixing and crushing the raw material and at thetime of crushing the temporarily baked material in order to cause Y₂O₃of 0.003 to 0.021 wt % and ZrO₂ of 0.06 to 0.37 wt % to contain thereinwith respect to all amounts in the oxide magnetic material by wear ofthe medium beads; and forming and baking the oxide magnetic materialcrushed by the medium beads and an internal conductor at temperature inthe range between 880° C. and 920° C.
 21. A method for producing anoxide magnetic material, said method comprising: mixing and crushing araw material with a media agitating mill of a wet internal circulationtype; temporarily baking the mixed and crushed material; and crushingthe temporarily baked material with the media agitating mill, wherein asilicon nitride is used as medium beads at the time of mixing andcrushing the raw material and at the time of crushing the temporarilybaked material in order to cause Si of 0.010 to 0.112 wt % to containtherein with respect to all amounts in the oxide magnetic material bywear of the medium beads.
 22. The method for producing the oxidemagnetic material according to claim 21, wherein diameter of the mediumbeads is in the range between 0.2 and 5 mm.
 23. The method for producingthe oxide magnetic material according to claim 21, wherein agitatingrate of the medium beads is in the range between 2.0 and 8.0 m/s. 24.The method for producing the oxide magnetic material according to claim21, wherein the material is crushed after temporarily baked so thatpowders of specific surface area of 6.0 to 15.0 m²/g are obtained.
 25. Amethod for producing a chip part, said method comprising: producing anoxide magnetic material, including: mixing and crushing a raw materialwith a media agitating mill of a wet internal circulation type;temporarily baking the mixed and crushed material; and crushing thetemporarily baked material with the media agitating mill, wherein asilicon nitride is used as medium beads at the time of mixing andcrushing the raw material and at the time of crushing the temporarilybaked material in order to cause Si of 0.010 to 0.112 wt % to containtherein with respect to all amounts in the oxide magnetic material bywear of the medium beads; and forming and baking the oxide magneticmaterial crushed by medium beads and an internal conductor attemperature in the range between 910° C. and 920° C.
 26. A method forproducing an oxide magnetic material, said method comprising: mixing andcrushing a raw material with a media agitating mill of a wet internalcirculation type; temporarily baking the mixed and crushed material; andcrushing the temporarily baked material with the media agitating mill,wherein a partially stabilized zirconia and a silicon nitride are usedas medium beads in order to cause Y₂O₃ of 0.001 to 0.011 wt %, ZrO, of0.03 to 0.194 wt %, and Si of 0.010 to 0.056 to contain therein withrespect to all amounts in the oxide magnetic material by wear of themedium beads.
 27. The method for producing the oxide magnetic materialaccording to claim 26, wherein the silicon nitride is included in therange between 20% and 99% in volume ratio with respect to the totalamount of the partially stabilized zirconia beads and the siliconnitride beads.
 28. The method for producing the oxide magnetic materialaccording to claim 26, wherein diameter of the medium beads is in therange between 0.2 and 5 mm.
 29. The method for producing the oxidemagnetic material according to claim 26, wherein agitating rate of themedium beads is in the range between 2.0 and 8.0 m/s.
 30. The method forproducing the oxide magnetic material according to claim 26, wherein thematerial is crushed after temporarily baked so that powders of specificsurface area of 6.0 to 15.0 m²/g are obtained.
 31. A method forproducing a chip part, said method comprising: producing an oxidemagnetic material, including: mixing and crushing a raw material with amedia agitating mill of a wet internal circulation type; temporarilybaking the mixed and crushed material; and crushing the temporarilybaked material with the media agitating mill, wherein a partiallystabilized zirconia and a silicon nitride are used as medium beads inorder to cause Y₂O₃ of 0.001 to 0.011 wt %, ZrO₂ of 0.03 to 0.194 wt %,and Si of 0.010 to 0.056 to contain therein with respect to all amountsin the oxide magnetic material by wear of the medium beads; and formingand baking the oxide magnetic material crushed by medium beads and aninternal conductor at temperature in the range between 910° C. and 920°C.